Prior to this invention, utilizable for metat sheet of thickness up to about 3/16 inch, applicant invented and patented a method set-forth in U.S. Pat. No. 4,281,786. However, for metal plate of a thickness of at least about 1/4 inch or more, that method does not work, failing to secure or lock-in a nut into an aperature into which it is inserted. Accordingly, applicant conducted extensive tests and experiments thereby making efforts and attempts to devise some other method for use with such metal plates of greater thickness.
Accordingly, the most relevant prior art is the inventor's own prior U.S. Pat. No. 4,281,786 which for metal plate of 1/4 inch or more thickness is inoperative and provides therefore no teaching for the present invention, even though there are similarities in the pressing apparatus and nut employed. It is the differences in the method and the particular diameters of the different portions of the nut, and the relative size of the nut to the holes of the aperature in the plate that obtain the success of the present invention as shall be described below.
Aside from the above-noted patent, even further irrelevant are such prior art patents as U.S. Pat. No. 3,399,705 to Breed et al., and Sowter U.S. Pat. No. 2,703,998. The Breed et al patent employs a nut having a downwardly-extending circumscribing nut-head flange which when the nut is pressed downward with its shaft in the aperature, causes sheet metal adjacent the aperature to be squeezed inwardly beneath the overhanging portion of the nut head and against the shaft of the nut positioned within the aperature space. The present invention does not require such a downwardly-extending nut-head flange. The Sowter patent, less relevant than applicant's own above-noted patent, does not relate at all to the mounting of an annular nut within an aperature; rather, the Sowter patent relates to securing a headed-shaft and is devoid of a stepped-shaft of the type required for the present invention, and thus is clearly non-teaching with regard to the solutions reached by applicant where such stepped nut-shaft structure is necessary. Moreover, even if all structures of the nut and press were fully disclosed as the prior art, the present invention requires the particular mounting method in order to obtain success, it has been ascertained during extensive experimentation arriving at the present invention. Accordingly the prior art to the present invention is not material.